1. Field of the Invention
The present invention relates to a polymerizable resin composition that enables water-repellent and ink-repellent treatment in a desired pattern, and more particularly to a resin composition that is capable of polymerizing by irradiation with ultraviolet light to form a coating in a desired pattern. The present invention also relates to a process for surface modification making use of such a composition, an ink jet recording head subjected to ink-repellent-treatment by the use of the composition, and an ink jet recording apparatus making use of the same.
2. Related Background Art
In various technical fields, there is commonly known a method of applying a water-repellent coating material to a member required to have water repellency or ink repellency so as to be endowed with such properties. Resin materials and coating materials used therefor have been developed.
As water- and oil-repellent coating materials, fluororesin- and silicone resin-type coating materials are most commonly available. Specifically, fluorine type coating materials having a fluoroolefin or perfluoro group are very stable both thermally and chemically, are excellent in weathering resistance, water resistance, chemical resistance, solvent resistance, or the like, and are also excellent in release properties, wear resistance and water repellency, thus they are widely used for various purposes. Silicone resins have good water repellency and oil repellency but have a low hardness alone, and, for this reason, are often combined with other types of resins such as acrylic resin, epoxy resin, urethane resin and so on or modified to make up coating material compositions.
Meanwhile, in the ink Jet (liquid jet) recording heads in which a liquid is discharged from discharge openings in the form of small droplets to cause the liquid to adhere to paper or the like to thereby perform recording or form images, there have been continued such improvement in performance as smaller droplets, higher driving frequency and a larger number of discharge openings in order to improve the recording characteristics. Accordingly, it has become more and more important to perform surface treatment of the discharge opening surface so that the surface state can always be kept constant with ease.
However, by use of such existing water- and oil-repellent coating materials, it is difficult to perform surface treatment of the discharge opening surface selectively, or precisely in a pattern, in such a way that the ink does not adhere to the surface. The reasons therefor are as follows:
(1) In order to impart properties like those of photoresists, a substance (compound) having a photosensitive functional group must be used as a main component. However, from the viewpoint of synthesis techniques, it is not easy to design molecules so that such a compound can have water repellency and ink repellency at the same time.
(2) The surface treatment of an ink jet recording head must be accomplished in a very small layer thickness of several xcexcm or less so as not to obstruct the function of minute nozzles. However, it is difficult to control the existing coating materials so as to have such a layer thickness.
In instances where the surface treatment has been attained by the existing fluorine type materials, the structure of coatings must be so designed as to be able to maintain the surface properties for a long term. However, most water- and oil-repellent materials have so low a coating hardness as to have a poor wear resistance, or may cause a lowering of water and oil repellency with occurrence of contamination and can be restored with difficulty in many cases. In this sense, they can not necessarily be satisfactory as materials for the surface treatment of discharge opening surfaces of ink jet recording heads.
Thus, at present, the ink discharge openings used in the ink jet recording system where an ink is ejected in the form of small droplets to effect recording are expected to have the characteristics shown below.
(1) The ink as the residue of ink columns having turned into droplets is held back immediately into the discharge opening.
(2) Ink droplets having adhered to the surface are swept out with ease by a cleaning operation.
(3) The discharge opening surface of the recording head is excellent in scratch resistance against the cleaning operation and paper carrying.
(4) In repeated liquid droplet formation and ink refilling, a meniscus is formed at the position of the discharge opening surface.
(5) The normal direction of the meniscus is in the direction of discharge.
(6) Even with a low surface tension of an ink used or under a small negative pressure, an interfacial tension, i.e., a contact angle, high enough to form a meniscus is retained.
(7) Since ink jet recording liquid is mostly adjusted to have a basicity of pH 7 to 11 for providing dissolution stability, structural materials are selected which can provide structural members with excellent alkali resistance and hydrolysis resistance.
The reason for requiring these characteristics is that, in the ink-jet recording head, any recording liquid such as ink which adheres to the circumference of the discharge openings directly affects printing performance in that it causes aberration in the discharge (flying) direction of liquid droplets discharged from the discharge openings to make it impossible to effect printing at a high precision.
As the prior art concerning the present invention, publications are available which disclose formation of a resin thin film by gas phase polymerization using a lacquer type fluororesin coating material, a fluorine type ultraviolet-curing coating material, a heat-curing fluororesin coating material, a fluorine type silane coupling agent or an epoxy resin composition having fluororesin particles dispersed therein.
For example, Japanese Patent Application Laid-Open No. 2-39944 discloses carrying out an ink-repellent treatment with a polymer having a fluoroacetyl group and a silazane group.
Such a coating material, however, could not necessarily achieve both water repellency and coating durability in some cases.
Japanese Patent Application Laid-Open No. 3-7781 also discloses an ink-repellent treating agent using a glycidyl ether derived from a fluorine type diol. A fluorine type epoxy resin disclosed therein was cured when used, and hence was advantageous in coating durability, but was not satisfactory in ink repellency.
Japanese Patent Application Laid-Open No. 6-328698 also discloses a method and a material for making openings with an excimer laser which is a breaking active energy ray. The method disclosed therein can achieve a superior processing precision and is useful for the production of ink-jet recording heads suited for the method, but may be applied with difficulty to an ink-repellent treatment using photolithography for attaining more precise processing.
Thus, under the existing circumstances, when the conventional materials and methods are adopted, no satisfactory surface treatment has been obtained which attains water-repellent and ink-repellent treatment with high precision and durability, and there is a continuing need for improvement.
An object of the present invention is to provide a resin composition for water-repellent treatment promising the above characteristics as coatings.
Another object of the present invention is to provide a fluorine-containing epoxy resin composition suited as a water-repellent agent or water-repellent coating material applied to places having opportunities of contact with solutions or materials containing components that may damage film forming properties or adhesion of water repellent agents, such as polar organic solvents, and also to provide an ink jet recording head endowed with a good ink repellency by the use of such a composition, and an ink jet recording apparatus using such a recording head.
A first embodiment of the resin composition of the present invention is a fluorine-containing epoxy resin composition comprising a fluorine-containing aliphatic epoxy resin comprising in one molecule at least one perfluoroalkyl group having 6-12 carbon atoms and at least two epoxy groups, and a cationic polymerization catalyst.
The term xe2x80x9cperfluoroalkylxe2x80x9d as used in the specification and claims refers to an alkyl group in which all the hydrogen atoms are substituted with fluorine atoms.
As the fluorine-containing aliphatic epoxy resin used in the present invention, there can preferably be used at least one of the compounds represented by the following general formulae (A-1) and (A-2): 
wherein Rf1 and Rf2 are independently selected from (CF2)nxe2x80x94CF3 or 
wherein n is 5-11 and m is 3-9;
and R1 and R2 are aliphatic groups.
A second embodiment of the resin composition of the present invention is a fluorine-containing epoxy resin composition comprising a fluorine-containing polyether resin comprising in a main chain an alicyclic hydrocarbon group comprising in a side chain at least one perfluoroalkyl group having 6-12 carbon atoms and at least two epoxy groups, and a cationic polymerization catalyst.
As the fluorine-containing polyether resin of the second embodiment of the resin composition of the present invention, there can preferably be used a polymer comprising an epoxy structural unit represented by the following general formula (D-1) or (D-2) and a perfluoro structural unit represented by the following general formula (D-3) or (D-4): 
wherein Rf is selected from CF3xe2x80x94(CF2)xxe2x80x94 or 
wherein x is 5-11 and y is 3-9;
and the total number of the structural units is 3-28.
The fluorine-containing aliphatic epoxy resin composition of the present invention may further contain as a compatibilizing agent, at least one of the compounds represented by the following formulae (C-1) and (C-2) as the occasion demands. 
Still another object of the present invention is to provide a surface treatment process for treating a surface of a substrate selectively, the process comprising successively:
the first step of applying the fluorine-containing epoxy resin composition of the present invention onto a substrate and drying the applied resin composition;
the second step of irradiating the applied composition with an activation energy ray in a pattern through a mask;
the third step of dissolving and removing a part of the applied composition not irradiated with the activation energy ray, by use of a liquid capable of dissolving the composition; and if desired
the fourth step of post-curing the remaining composition.
Yet another object of the present invention is to provide a surface treatment process for treating a surface of a substrate selectively, the process comprising successively:
the first step of applying the fluorine-containing epoxy resin composition of the present invention onto a substrate and drying the applied resin composition;
the second step of heating or irradiating with an activation energy ray the applied composition to effect polymerization and curing over the whole area thereof;
the third step of selectively irradiating the cured composition with a breaking activation energy ray to partly remove the cured composition; and if desired the fourth step of post-curing the remaining composition.
Yet still another object of the present invention is to provide an ink jet recording head having a discharge opening surface with a discharge opening for discharging a recording liquid therethrough, wherein at least a discharge opening formed portion of the discharge opening surface is coated with a cured film comprising the fluorine-containing epoxy resin composition of the present invention, and an ink jet recording apparatus comprising the ink jet recording head.
Since the resin composition of the present invention is of an epoxy resin type, it has an excellent adhesion to various members, can be cured at a relatively low temperature, and can provide a cured product having excellent physical properties as a structural member. Further, since the epoxy compound having a perfluoro group at the terminal is contained, the resin composition is improved greatly in resistance to water-soluble organic solvents, in particular, to polar organic solvents. Moreover, the action of a compatibilizing agent makes the components compatible with one another, so that the scope of material constitution can be broadened.
The fluorine-containing epoxy resin composition of the present invention is useful as a material applied to places having opportunities of contact with solutions or materials containing components that may decrease the adhesion of water repellent agents, such as polar organic solvents. As a water-repellent material or water-repellent coating material used on such places, the present resin composition is especially suited for water-repellent and ink-repellent treatment of discharge opening surfaces of ink jet recording heads.
In the ink jet recording apparatus of the present invention, the employment of selective surface modification utilizing photopolymerizability enables highly precise treatment, and constituting the cured film of specific materials can provide water-repellent or ink-repellent areas having superior solid strength and anti-friction strength.